The report describes progress made in the development of a system for the automatic detection of bubbles by digitally processing Doppler ultrasonic signals. The system was developed primarily because of the need for an objective means of counting bubbles in the blood of divers, aviators, or other individuals who have been subjected to a reduction in ambient pressure. The number of bubbles is thought to indicate the stress felt by an individual as a result of the decompression. The characteristics of the signals are described, and the theory underlying the development of the algorithm is developed. The results of tests of the algorithm on various signals are presented. The algorithm is successful at detecting the presence of bubbles when they are moderately frequent, but does not distinguish infrequent bubbles from normal cardiac signals, and fails to distinguish bubbles when they are extremely numerous. To deal with the latter case, pattern matching should be used.